[Role of dendritic cells in the pathogenesis of severe pneumonia in children].

Objective: Severe pneumonia is one of the common severe diseases in children. Increasing evidences show that immune response greatly contribute to severe pneumonia. Dendritic cells (DC) are the important antigen presenting cells in the lung. To study the role of dendritic cells in development of severe pneumonia in children, the authors measured the number of mature DC in bronchoalveolar lavage fluid (BALF), and evaluated the relationship among IL-12, pro-inflammatory cytokines and clinical scores.

Methods: The following 3 groups of children were enrolled in this study: severe pneumonia group: 27 children with severe pneumonia treated between November 2002 and May 2003 in PICU; mild pneumonia group: 30 children with mild pneumonia in department of pulmonology; control group: 29 children without pneumonia but receiving ventilator treatment for chest surgery. Mature DC in BALF was determined in severe pneumonia group and the control group on the day of tracheal intubation for mechanical ventilation. Acute lung injury scores and severe disease scores were evaluated in children with severe pneumonia and mild pneumonia. All children's serum levels of TNF-alpha, IL-6 and IL-12 were measured by using ELISA within 24 hours after admission. SPSS version 11.5 was used for statistical analysis.

Results: (1) The percent of mature DC in children with severe pneumonia was significantly higher when compared with the control group on the first day after ventilation [14.2 (3.9 - 51.8)] vs. [1.3 (0.2 - 22.5)] (Z = 5.44, P < 0.01). (2) In severe pneumonia group, the concentration of serum IL-12 [117.0 (79.9 - 159.4) ng/L], TNF-alpha [90.6 (52.2 - 185.9) ng/L], IL-6 [128.7 (73.3 - 793.8) ng/L] were significantly higher than those in mild pneumonia group where the values were [71.6 (19.4 - 196.8)], [26.6 (2.5 - 113.9)], and [39.9 (7.8 - 82.5)] (P < 0.01), and the control group [6.4 (12.2 - 92.0)], [6.4 (1.8 - 91.9)], and [23.0 (6.4 - 54.2)] (P < 0.01). Serum IL-12, TNF-alpha and IL-6 levels in children with mild pneumonia were higher than those of control group (P < 0.01). (3) The percent of mature DC was increased with the serum level of IL-12 (r = 0.48, P < 0.01), TNF-alpha (r = 0.58, P < 0.01), IL-6 (r = 0.51, P < 0.01) and lung injury scores (r = 0.39, P < 0.05), but it did not correlate with severe disease scores (r = -0.11, P > 0.05).

Conclusions: There is excessive production of pro-inflammatory cytokines and over-stimulation of lung dendritic cells in children with severe pneumonia. Over-stimulation of lung dendritic cells, the increased serum levels of IL-12, TNF-alpha, IL-6 and the severity of pneumonia may suggest that DC plays an important role in pathogenesis of severe pneumonia in children.